The present invention relates to a signal processing device, a signal processing method, and a program. In particular, the present invention is preferably applicable to an orthogonal frequency division multiplexing receiver (OFDM receiver).
For an OFDM receiver used, for instance, for communication and broadcasting, a fast Fourier transform (FFT) is generally used. A signal received by the OFDM receiver has a spectrum that exhibits an impulsive peak periodically at intervals of subcarrier frequency. Therefore, demodulation is achieved by using the FFT to calculate the intensity of the signal at a frequency equivalent to the intervals of subcarrier frequency. As is well known, the FFT is a process in which a matrix operation is performed on a finite number of time-series data. More specifically, the FFT is an algorithm that assumes a waveform in which the finite number of time-series data are periodically repeated, and rapidly calculates a frequency component that is obtained when the waveform is Fourier-transformed. In reality, however, the signal actually input to the FFT cannot be expected to be a waveform that is repeated at intervals of the number of time-series data (FFT length), which is an input to the FFT. Nevertheless, the FFT makes the above assumption. It means that a waveform in which discontinuity occurs at joints between the finite number of time-series data is assumed to be an input signal. Thus, a frequency component derived from waveform discontinuities leaks into a normal frequency component. As a result, a so-called leakage error occurs. It is known that preprocessing is performed before the FFT to execute a window function in order to suppress the leakage error. For example, a Blackman-Tukey window function is well known. When a finite number of time-series signals for FFT are obtained from a sequence of time-series signals and subjected to a weighting process, the above-mentioned window function suppresses the leakage error by alleviating the discontinuities at the joints.
A technology disclosed in WO/2009/031239 enables an OFDM receiver having an FFT circuit preceded by a window function processing section to eliminate an interfering wave while performing a window function process to suppress the deterioration of a bit error rate (BER). A desired-to-undesired signal ratio (D/U ratio) measurement section is incorporated in the OFDM receiver to change the coefficients of the window function process in accordance with a measured D/U ratio. As described in FIGS. 8 and 9 and in paragraphs 0055 to 0057, the window function process is performed by selecting one window function coefficient set from two different window function coefficient sets in accordance with the measured D/U ratio. Consequently, the interfering wave can be successfully eliminated.